PC680 failure: What's killing my batteries?

Having experienced my second PC680 failure today, my airplane is now on it's 3rd battery in 12 months.

Both failures were identical: the battery was working perfectly, and then the next time I pulled the plane out, it refused to start. The battery would pull a couple blades through, then click-click-click on the solenoid. Putting the approved Odyssey charger (6Amp) on the battery, it ran right up to "charged" on about 10 seconds.

When the original battery failed, I wrote it off as a leftover injury from several "oops, left the power on" episodes during building, which ran the battery completely dead. With this second identical failure, I'm wondering if there isn't something else at work.

I've read the previous big thread on this failure mode, which ended up focusing on a pattern of charger use that I don't follow. This battery has never seen the charger, only charged by the alternator after start. My PP alternator holds the bus voltage at 14.6 volts, which is in line with Odyssey's recommendation for 14.5+. Review of data logs show nothing unusual in amps or volts readings from the previous flights. (Previous flight was 6 days earlier.)

The displayed voltage on the bus prior to a start attempt was 12.6V, and it drops to 8.4V during start, when the solenoid drops out. I took the battery for a load test at Batteries Plus, who said it was giving less than 50% of it's rated output. This battery was installed 30 Hobbs hours ago, in March '13. The master switch completely disconnects the battery -- there are no parasitic/keep-alive loads.

I came home with a new battery, which I'll install tomorrow, and I expect everything will operate normally as it did before. Given the sudden and warning-less nature of the failure, it sure would be ideal to have an explanation other than "it happens." Heat? Vibration? The mounting is Van's box, installed per plans.

They don't seem to recover well from a complete discharge, ask me how I know! Having said that I am on my third battery in 9 years, so your experience is not normal. The times mine went bad were my fault because I left the master ON.

After watching the video about the company, I would be getting in touch with that fella !

It seems they are pretty slick on customer service and I am sure they would investigate.

It's sounds like something is pulling a draw on the battery even after you shut down. Do you have a charging port or some other port installed that is wired direct to the battery? Even if nothing is plugged into it, it still will draw power from the battery. It's like leaving your phone charger plugged into the wall, even though your phone isnt plugged Ito it, it still is drawing power.

Years ago, a GM engineer that worked with battery validation told me that if a lead acid battery gets discharged once, the life is halved, twice, get a new one.

Maybe there is something different about these AGM's, but it is the same basic lead/acid chemistry. Definitely check for static current draws and with the factory regarding the charging technicalities.

Curious if you have electronic ignition and if so is there a switch to turn it off. The instructions on mine werre pretty vague on an on/off switch because I used a key switch. It took a while to figure out that the EI was still technically on even though the key switch was off. Installed a switch and no more problems with battery discharge.

Ok,

If this second battery was never ran all the way down. (They can be revived if ran all the way down if you follow the procedure on the website)

and

You are sure you don't have parasitic loads...

How long do you typically fly after a start? It takes a while to fully charge one of these batteries after a start.

Your failures appear to be just like mine which are caused by the battery not being stored in a fully charged state causing sulfidation of the plates. In my case I assumed the recommended charger was smart enough to do the job but it was not.

If you follow the procedure listed in the other thread, most likely you can revive your second battery to almost like new condition.

C-FAH Q said:

It's sounds like something is pulling a draw on the battery even after you shut down. Do you have a charging port or some other port installed that is wired direct to the battery?

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Nothing; the only thing that comes off the battery is the fat wire to the battery contactor, and the 8" pigtail for connecting the battery charger. Unless there's something internal to the contactor that is faulted and leaking current; but the plane has been left to sit for longer than 6 days previously, and the battery was as strong as ever, unlike this recent failure. When I take it apart for the condition inspection later this month, I'll put an ammeter inline with the master off, to verify nothing's drawing current.

Capflyer said:

Curious if you have electronic ignition and if so is there a switch to turn it off. The instructions on mine werre pretty vague on an on/off switch because I used a key switch.

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Dual P-mags, with toggle switches that do interrupt ship's power to the ignition, not just the P-lead.

Brantel said:

How long do you typically fly after a start? It takes a while to fully charge one of these batteries after a start.
Your failures appear to be just like mine which are caused by the battery not being stored in a fully charged state causing sulfidation of the plates.

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It's rare that I take the plane out for less than an hour when I go flying. The day of the trip previous to the failure was a total of 3.2 hours; the final leg being 1.1. FWIW, here's a graph of B-lead amps and bus volts for the first 20 minutes of flight...it stabilizes pretty quickly after start. (The plateau at :04 - :06 is the boost pump running.)

Brantel said:

If you follow the procedure listed in the other thread, most likely you can revive your second battery to almost like new condition.

Click to expand...

Unfortunately, Batteries Plus took the bad one for a core. I do still have the original one that died in March, though, and I'm going to follow the procedure you posted to see if that one can be revived as a test...it can be a tractor battery or something if it lives again.

My PC680 battery failed from a poor internal weld.
Read about it on the AeroElectric List.
Bob Nuckolls' ANALYSIS.
Bob's PICTURE of failed weld.

RV7AV8R said:

Having said that I am on my third battery in 9 years, so your experience is not normal. The times mine went bad were my fault because I left the master ON.

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I am still on my first and original battery and in the eight year. I live mine on the charger all the time, unless I am traveling and not in my own hanger. Have not had any issues with it.

It's pretty easy to see if you have something draining the battery after the master is off. Just remove either the + or - terminal from the battery and put an AMP meter on the end and the post. It will show 0 or some draw. Switch the meter down from the highest setting down the the lowest, one at a time, and see if there's anything. If so, trace it down. An Odyssey battery should hold a near full charge quite a long time and last for 4 + years normally.